On Fri, Apr 24, 2009 at 12:16:06AM +0200, Erik Quaeghebeur wrote:
m = mapM (\x -> [(x,-1),(x,0),(x,1)]) ['a','b','c'] map (\x -> snd $ unzip x) m
Any more direct way of doing this?
On Fri, Apr 24, 2009 at 11:36:44AM +0100, Jan Jakubuv wrote:
Well, you can write:
mapM (const [-1,0,1]) [1..3]
On Fri, 24 Apr 2009, Brent Yorgey wrote:
Better yet (in my opinion), you can just write
sequence (replicate 3 [-1,0,1])
which is really the same thing, since mapM = sequence . map. Mapping (const [-1,0,1]) over [1..3] yields [[-1,0,1], [-1,0,1], [-1,0,1]], that is, (replicate 3 [-1,0,1]). It's the 'sequence' that does the magic of selecting an item from each of the three lists in all possible ways.
Yes, now I see it, thanks to both Jan and Brent. I can nicely generalize this to n = ... values = [...] sequence (replicate n values) My ideas about how I should approach other aspects of my programming task are also crystallizing. Now find a nice stretch of time to work things out... Erik